metronome

metronome (mĕˈtrənōmˌ) [key], in music, originally pyramid-shaped clockwork mechanism to indicate the exact tempo in which a work is to be performed. It has a double pendulum whose pace can be altered by sliding the upper weight up or down. The sliding bob indicates the rate of oscillation by means of calibrations on the pendulum. A number to indicate the rate at which the metronome is to be set and a note whose value is to equal one beat of the metronome are often given on a piece of music, preceded by the initials MM, for Mälzel's Metronome—Johann Mälzel (1772–1838) having made in 1816 the type of metronome in general use today. Beethoven and Schumann left such tempo indications for many of their compositions, but for earlier music and often for later music such indications are those of the editor. A pocket-watch type of metronome was developed in the 1940s; a boxlike electric metronome has also become popular, as well as digital metronomes.